This invention relates to an electronic tuning receiver and more particularly to an electronic tuning receiver in which the rate of sweeping the local oscillation frequency of a local oscillator is controlled in association with alternative selection of Distance mode reception or LOCAL mode reception.
In the conventional electronic tuning receiver, a sweep rate control knob and a Distance receiver/LOCAL receiver mode selector switch are individually installed on a receiver operational panel so that it is impossible to select from the Distance and LOCAL receiver modes by the movement of the sweep speed control knob. In other words, after the Distance/LOCAL receiver mode selector switch is turned to the Distance receiver mode side, for example, sweep operation is initiated at a maximum rotation position of the sweep speed control knob and thus at a high speed upon the rotation of the sweep speed control knob. The operator's careful attention must be paid to listen to broadcasting signals with the resulting difficulty in the tuning operation during the Distance (weak intensity and long distance) receiver mode in which the broadcasting signals are substantially small and weak.
On the other hand, the broadcasting signals are relatively strong and thus the tuning operation relatively easy even during the high speed sweep operation of the LOCAL (strong wave and short distance) receiver mode. However, a slow sweep operation prolongs the period of time required for completing the tuning operation. While it is desirable to install a Distance/LOCAL receiver mode selector responsive to the sweep speed on the receiver panel, this is impossible as a matter of fact. However, provided that the broadcasting signals are equal in level during both the DX receiver mode and the LOCAL receiver mode, the actuation of only the mode selector can achieve the optimum tuning operation.
For car radio receivers in which the location thereof constantly varies with respect to respective broadcasting stations, it is technically difficult to equal the broadcasting signal level during the tuning operation for both the Distance receiver mode and the LOCAL receiver mode. The sweeping speed therefore must vary in accordance with whichever one of the Distance mode or the LOCAL mode is active, in order to achieve prompt and accurate tuning operation.
Moreover, there are various requirements for the installation of car radio receivers on an instrument mount panel in front of the driver's seat, the radio receivers being limited in shape and size depending upon different types and makes of vehicles. The sweep speed control knob and the Distance/LOCAL mode selector should be mounted in relation with other operating switches and knobs. An increase in the number of switches and knobs on radio receivers mounted in these vehicles is undesirable to safe driving.